According to the prior art, automatic transmissions, in particular for motor vehicles, comprise planetary gearsets, which are shifted by way of frictional elements or shifting elements, such as possibly clutches and brakes, and are usually connected to a starting element that is subjected to a slip effect and is selectively provided with a lockup clutch, such as a hydrodynamic torque converter or a fluid clutch.
A transmission such as this is disclosed in EP 0 434 525 A1. It comprises essentially an input shaft and an output shaft, which are arranged parallel to each other, a double planetary gearset arranged concentrically with the output shaft, and five shifting elements in the form of three clutches and two brakes, whose selective engagement in pairs determines the various gear ratios between the input shaft and the output shaft. The transmission comprises a front-mounted gearset and two power paths, so that six forward gears can be achieved by selectively engaging, in pairs, the five shifting elements.
Two clutches are required, in the first power path, for the transmission of torque from the front-mounted gearset to two elements of the double planetary gearset. In the direction of power flow, these are arranged essentially behind the front-mounted gearset in the direction of the double planetary gearset. With the second power path another clutch is provided, which detachably connects this to another element of the double planetary gearset. The clutches are arranged in such a way herein that the inner disk carrier forms the output.
A compact multi-speed transmission of planetary construction, in particular for a motor vehicle, which comprises two planetary gearsets and one front-mounted gearset, as well as three clutches and two brakes, is also known from U.S. Pat. No. 6,139,463. In this known multi-speed transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting torque from the front-mounted gearset to the two planetary gearsets. Here, the outer disk carrier and/or the cylinder or piston and pressure compensating side of the clutch C-3 is connected to a first brake B-1. In addition, the inner disk carrier of the third clutch C-3 is connected to the cylinder or piston and pressure compensating side of the first clutch C-1, wherein the inner disk carrier of the first clutch C-1 is arranged on the output side and is connected to a sun gear of the third planetary gearset.
From DE 199 49 507 A1 of the applicant a multi-speed transmission is additionally known, in which two non-shiftable front-mounted gearsets are provided on the input shaft, which generate two rotational speeds on the output side, which, in addition to the rotational speed of the input shaft, can be optionally shifted to a shiftable double planetary gearset that acts on the output shaft by selectively engaging the shifting elements that are used in such a way that, in order to shift from one gear to the next higher or lower gear, only one shifting element of the two just actuated shifting elements has to be engaged or disengaged.
From DE 199 12 480 A1 an automatically shiftable motor vehicle transmission is known, which comprises three single carrier planetary gearsets as well as three brakes and two clutches for shifting six forward gears and one reverse gear, and one input shaft and one output shaft. The automatically shiftable motor vehicle transmission is designed in such a way that the input shaft is connected directly to the sun gear of the second planetary gearset, and the input shaft can be connected to the sun gear of the first planetary gearset by way of the first clutch and/or to the carrier of the first planetary gearset by way of the second clutch. In addition or as an alternative, the sun gear of the first planetary gearset can be connected to the housing of the transmission by way of the first brake and/or the carrier of the first planetary gearset can be connected to the housing by way of the second brake and/or the sun gear of the third planetary gearset can be connected to the housing by way of the third brake.
Furthermore, from DE 102 13 820 A1 an automatic multi-speed transmission is known, which comprises a first input path T1 of a first gear ratio; an input path T2, which has a greater gear ratio than the input path T1; a planetary gearset with four elements, wherein the four elements are a first element, a second element, a third element, and a fourth element in the sequence of the elements in a speed diagram; a clutch C-2, which transmits a rotation of the input path T2 to the first element S3; a clutch C-1, which transmits the rotation from the input path T2 to the fourth element S2; a clutch C-4, which transmits a rotation from the input path T1 to the first element; a clutch C-3, which transmits the rotation from the input path T1 to the second element C3; a brake B-1, which induces the engagement of the fourth element; a brake B-2, which induces the engagement of the second element; and an output element, which is coupled to the third element R3.
Within the scope of DE 101 15 983 A1 of the applicant a multi-speed transmission is described, which comprises an input shaft that is connected to a front-mounted gearset, an output shaft that is connected to a rear-mounted gearset, and a maximum of seven shifting elements, whose selective shifting allows at least seven forward gears to be shifted without a range shift. The front-mounted set is comprised of a front-mounted planetary gearset or a maximum of two non-shiftable front-mounted planetary gearsets that are coupled to the first front-mounted planetary gearset, wherein the rear-mounted gearset is designed as a two-carrier, four-shaft transmission with two shiftable, rear-mounted planetary gearsets, and has four free shafts. The first free shaft of this two-carrier, four-shaft transmission is connected to the first shifting element; the second free shaft is connected to the second and third shifting elements; the third free shaft is connected to the fourth and fifth shifting elements; and the fourth free shaft is connected to the output shaft. For a multi-speed transmission with a total of six shifting elements, it is proposed according to the invention to additionally connect the third free shaft or the first free shaft of the rear-mounted gearset to a sixth shifting element. For a multi-speed transmission with a total of seven shifting elements, it is proposed according to the invention to additionally connect the third free shaft to a sixth shifting element D′ and to additionally connect the first free shaft to a seventh shifting element.
A multi-speed transmission with at least seven gears is further described within the scope of DE 101 15 987 of the applicant. This transmission consists, in addition to the input shaft and the output shaft, of a non-shiftable front-mounted gearset and a shiftable rear-mounted gearset in the form of a two-carrier, four-shaft transmission. The front-mounted gearset consists of a first planetary gearset which, in addition to the input rotational speed of the input shaft, offers a second rotational speed, which can be optionally transferred to a rear-mounted gearset. The rear-mounted gearset consists of two shiftable, planetary gearsets, which can shift into at least seven gears using the six shifting elements, whereupon two power paths are formed. Range shifts are advantageously always prevented during each shifting operation. A 9-gear multi-speed transmission is furthermore known from DE 29 36 969; it comprises eight shifting elements and four gearsets.
Automatically shiftable motor vehicle transmissions of planetary construction have been described multiple times in the state of the art and are subject to continuous development and improvement. These transmissions should have a sufficient number of forward gears as well as one reverse gear and a gear ratio, well suited for motor vehicles, with a high overall transmission ratio spread as well as favorable progressive ratios. They should further enable a high starting gear ratio in the forward direction and should contain a direct gear, and should be suitable for use in both passenger vehicles and commercial vehicles. In addition, these transmissions should require a low construction costs, in particular, require a small number of shifting elements and should prevent double-shifting when shifting sequentially so that only one shifting element is engaged when shifting into defined gear groups.
It is the object of the invention to propose a multi-speed transmission of the kind described above, in which the construction cost is low and the efficiency of the main travel gears is also improved in terms of drag and gearing losses. A low torque should act on the shifting elements and planetary gearsets and the rotational speeds of the shafts shifting elements, and planetary gearsets should also be kept as low as possible with the multi-speed transmission of the invention. Furthermore, the number of gears as well as the spread of transmission ratios should be increased, so that seven forward gears and at least one reverse gear can be advantageously implemented. The transmission of the invention should also be suited for any vehicle design, especially for a front-transverse arrangement.